Circle $O$ is located on the coordinate plane with center at $(2,3)$.  One endpoint of a diameter is at $(-1,-1)$.  What are the coordinates of the other endpoint of this diameter?  Express your answer as an ordered pair.
Solution: [asy]
draw((-7,0)--(11,0),Arrows);
draw((0,-5)--(0,11),Arrows);
label("$x$",(12,0)); label("$y$",(-1,11));
draw(Circle((2,3),5));
dot((2,3)); dot((-1,-1));
label("(2,3)",(2,3),W);
label("(-1,-1)",(-1,-1),W);
draw((-1,-1)--(2,-1),dashed+red); draw((2,-1)--(2,3),dashed+blue);
draw((2,3)--(5,3),dashed+red); draw((5,3)--(5,7),dashed+blue);
dot((5,7));
label("(?,?)",(5,7),E);
[/asy]

Refer to the above diagram.  Since the opposite ends of a diameter are symmetric with respect to the center of the circle, we must travel the same distance and direction from $(-1,-1)$ to $(2,3)$ as we do from $(2,3)$ to the other endpoint.  To go from $(-1,-1)$ to $(2,3)$ we run $3$ (left dashed red line) and rise $4$ (left dashed blue line), so our other endpoint has coordinates $(2+3,3+4)=\boxed{(5,7)}$.